The present invention relates to fiber formation, and more specifically, to fiber formation from a molten substrate.
Printed circuit boards are often made with a mat of woven glass fibers within a cured resin substrate. The glass fibers provide structural reinforcement for the resin. The glass fibers are formed by extruding molten glass. Occasionally, a bubble in the molten glass is carried into the extrusion process. In such cases, the bubble can be contained in a formed thread in an elongated form. As a result, the thread includes a hollow region.
If such a hollow thread is used in a printed circuit board, the hollow thread could cause a circuit failure, such as a short circuit or an open circuit. For example, holes or vias are often drilled through a printed circuit board. If such a hole is drilled through a hollow thread, a conductive circuit material could travel through the hollow portion of the thread, forming a conductive anodic filament (CAF). The CAF could inadvertently connect two circuit elements that are not supposed to be connected, resulting in a short circuit or bad circuit.
As the density of circuit elements on printed circuit boards increases, the likelihood that a hollow thread will cause a circuit failure also increases. Thus, avoiding the use of hollow threads in printed circuit boards is important to reduce the number of faulty circuit boards. Currently, random samples of formed glass threads are pulled from production and checked for hollow threads. In the event a hollow thread is discovered, the sample and at least a portion of a batch from which the sample came are discarded. Such random sampling is imperfect because a hollow thread could make it through the process undetected. Furthermore, such a process could result in large amounts of scrap thread when thread is discarded due to a discovered hollow thread.